Method of producing printing plates



Dec. 3, 1957 R. R. MYERS, JR 2,814,990

METHOD OF PRODUCING PRINTING PLATES Filed July 12. 1954 ML w Anvmlor 30Qoberl' Qwzrs Jr. W1 raw: W

dll'i'arngys 2,814,990 METHOD or PRODUCING PRINTING PLATES Robert R.Myers, Jr., Chicago, Ill.

Application July 12, 1954, SerialNo. 442,806

Claims. ((31. 101-401.1)

This invention relates to the art of manufacturing printing plates andmore particularly to laminated printing plates. The printing plate andmethod of making the same is an improvement on the one disclosed in myco-pending application for United States Letters patent on a method ofmaking printing plates, filed November 6, 1953, Serial No. 390,579.

The present method of making printing plates is slow and tedious. Theprepared printing shells are inverted and subjected to molten backingmaterial. This build up of the shell is relatively thick and after ithas cooled and solidified it then must be trimmed and planed to thecorrect thickness. Obviously equipment for performing this necessaryprocess is expensive, usually eliminating this plate preparation fromthe smaller shop due to the capital investment necessary. Furthermore,there are many diificulties attendant to the manufacture of theconventional printing plate. One objection is the relatively heavyweight of the finished printing plate. One reason for this is that toobtain strength in the plate it is necessary that the backing materialbe of maximum thickness. The backing material is, of course,exceptionally heavy due to its volume. Most: backing material isapproximately ninety-four percent (94%) lead, three percent (3%) tin,and three percent (3%) antimony. While the backing material is thus of avery heavy nature, it is not strong and obviously has the possiblecharacteristic of bending. Still another problem is that the finishedplates have their edges beveled and are held to the press by inverselybeveled clamp members. Obviously due to the softness of the backingmaterial, these clamp members may penetrate the plate resulting in theplate becoming loose on the press and buckling and breaking. Thiscombination of objections in the common printing plate places manyrestrictive limits on the speed on which the press may be operated. Inthe case of rotary presses, the weight of the plates cause centrifugalforce to build up rapidly with the result that the plates tend to bendoutwardly and either break or produce undesirable, irregular printing.Still another objection to the common printing plate is the time aspect.Considerable time must be taken in permitting the backing material tocool after it has been placed on the shell. Furthermore, the shavingand. planing of the printing plate is not only time consuming butrequires the services of skilled operators.

Therefore, the principal object of my invention is to provide a methodof making printing plates that produce a relatively light and strongprinting plate and one of minimum thickness.

A still further object of my invention is to provide a laminatedprinting plate using a perforated metal sheet and a. plastic sheet thatmore successfully secures the plastic sheet to the perforated metalsheet.

A further object of my invention is to provide a method of makingprinting plates that often eliminates the necessity of shaving the plateto obtain the proper thickness prior to installation on the press.

A still further object of my invention is to provide the Patented Dec.3, 1957 method of making a printing plate which embraces the idea oflaminated printing plate with one lamination being of irregular plasticsheet so that the plastic will be of uniform strength and densitythroughout the printing plate area.

A still further object of my invention is to provide a light weightstrong printing plate that may be produced rapidly thereby saving inboth labor, time and materials.

A still further object of my invention is to provide a method of makingprinting plates that requires a minimum of equipment.

These and other objects will be apparent to those skilled in the art.

My invention consists in the method or process, whereby the objectscontemplated are attained as hereinafter more fully set forth, pointedout in my claims, and illustrated in the accompanying drawings, inwhich:

Fig. l is an enlarged edge view of a printing shell,

Fig. 2 is an enlarged edge view of the printing shell and a relativelythin backing material imposed thereon,

Fig. 3 is an enlarged edge view of the: unit shown in Fig. 2 with alayer of adhesive thereon,

Fig. 4 is an exploded edge view of my printing plate consisting of aprinting shell backing material, a layer of adhesive material, a layerof plastic, a layer of adhesive material, and a plate prior to beingcompressed into a finished printing plate,

Fig. 5 is an enlarged view of a portion of my perforated metallic sheet.I

Fig. 6 is an enlarged cross-sectional view of a portion of theperforated metallic sheet showing an adhesive on one side thereof andpenetrating into the holes thereof.

Fig. 7 is a diagrammatic side view of the step of heating a plate priorto compression.

Fig. 8 is a diagrammatic side view of a flat plate being compressed tothe proper thickness.

Fig. 9 is an enlarged cross-sectional view of a portion of my plateafter being compressed and prior to trimming, and,

Fig. 10 is a diagrammatic side view of an arcual plate being compressedto the proper thickness.

To clarify the structure of a finished printing plate, I shall firstexplain the steps necessary to produce the complete plate as shown inFig. 9, it being understood, however, that this invention is only a partof such finished plate.

While I have indicated and will describe my invention as not needing thethinning and shaving of the backing material from the shell, there wellmay be times and'circumstances when it will be desirable to smooth andreduce the shell backing material by suitable means.

The numeral 14) designates the ordinary printing shell having theprinting indicia thereon. If this shell is very thin, it may be backedwith a suitable backing material 12. However, the thickness of thisstrengthening soft metal 12 is relatively thin, as opposed to therelatively heavy thick backing material heretofore used. An adhesive 14is then applied to the surface of the backing 12. Next in the finishedlaminated printing plate is my printing plate back which consists of athermoplastic sheeet 15, a metal sheet 18, and an adhesive 20 that isused betweenthe plastic and metal sheet as shown in Fig. 4. Thisthermoplastic may be any one of several that have been devel-' oped suchas vinyl acetate-vinyl chloride material. The named material hasexcellent dimensional stability char acteristics and will not shrinkafter it is compressed. A sheet 18 may be of any metal that can be maderather rigid such as steel, alloys of copper, alloys of aluminum, andZinc. I consider aluminum alloy the best material, because it is lightin weight yet strong. I realize that some: of the alloy steels can beequally strong or stronger for the same weight, but in this case we arealsofaced with a need to have a sheet of particular thickness as well.For the one-fourth inch A1") plate, the sheet metal should beapproximately one hundred twenty thousandths of an inch in thickness.This thickness requirement means that the aluminum alloy retains aweight advantage over sheet steel. The steel, of course, is stronger sothat with a balanced press. drum, the steel could be nearly asadvantageous as aluminum alloy. The plastic face of my unit is thenplaced adjacent the adhesive 14. The assembled plate is then suitablyheated to render the thermoplastic compressible. After heating, theassembled plate is placed in a mold press of limited travel. Thistravelof the press indicates the thickness of the printing plate desired.Inasmuch as the heated plastic is compressible, it is squeezed down toallow for the differences and therefore extends into and occupies any ofthe irregularities of the plate or sheet, and also permits the over alldesired thickness in the plate. Therefore, it is obvious that it is notimportant for the shell or the sheet metal to be perfect in surface northickness prior to being compressed in the mold.

I have found that if the metal sheet used is of solid sheet material,gases will be objectionably trapped and also any vertical contraction ofthe sheet in the mold press affects the entire sheet. The reason forthis is that when the plastic sheet is compressed, any surplusencountered at a given point must flow to another location or out at thesides of the plate. This means that the plast1c must be heatedsulficiently to permit relatively long d1stortions, i. e., if thegreatest compression were near the center of the plate, the plasticsheet would obviously have to be effected and moved to the furthestdimensions of the plate. Obviously this would mean that the density ofthe plastic sheet would not be consistent throughout its area. Not onlyWould this make for an uneven plate and be objectionable, but theplastic would have to be heated to such temperature that it wouldreadily flow to the far reaches of its dimensions. Furthermore, a platewill not cool evenly and we might well have a situation Where the edgesof the plastic would solidify and harden prior to the absorption ofsurplus plastic material at the center of the plate.

I have overcome these objections and problems by providing the sheet 18with a series of holes 22 throughout its surface as shown in Fig. 5. Irecommend that this sheet 18 be approximately twenty to thirty percentopen. When such a sheet is compressed in the mold press, any surplus ofplastic encountered has an immediate route of escaping by filling thehole areas. Obviously, when such a plastic sheet is used, any givenpoint or area that requires a compressing of the plastic to make theplate will be done immediately within that vicinity without affectingthe balance of the plastic sheet area.

In most areas of the metal plate, if not all, the plastic will enter theholes 22 as shown in Fig. 9. The chief problem, of course, of all suchlaminated printing plates is to weld the plastic sheet to the perforatedmetal sheet. The accomplishment of this problem is the heart of thisinvention. In placing the adhesive 20 on the perforated plate or metalsheet 18, I not only coat the inner side of the metal with a suitableglue or adhesive but cause the adhesive to run into and coat the wallsof the holes 22, as shown in Fig. 6. Thus when the plate is finished theplastic that does penetrate the holes of sheet 20, will be glued andheld therein as shown in Fig. 9. This feature is most important. When alaminated plate is so formed, the plastic and metal sheet will notseparate even under severe usage.

In the drawings I have shown the various laminations of considerablethickness, but this is only illustrative and enlarged for purposes ofidentification. The thermoplastic sheet should be approximately fifteenthousandths to twenty thousands of one inch.

The plate that is made by my method is very clearly much lighter than aconventional plate. The plastic and sheet metal comprise more thanone-half of the total thickness of the plate. The plastic and the sheetmetal each have a specific gravity much less than that of the backingmetal that is more than nine-tenths lead. Furthermore, the sheet metalhas more rigidity than a lead plate of the same thickness. The lead thatcomprises the usual backing is also far surpassed in rigidity by thealuminum alloy or steel sheet used in my method. As a result, I haveboth a stronger plate and a lighter one. These two facts mean apotentially substantial increase in safe press speed. By reducing theweight of the plate, I have lessened the total centrifugal force createdat a given speed, and the strong plate resists better the tendency ofthe centrifugal force to tear the plate from the press drum than doesthe usual lead-antimony-tin alloy backing used in conventional plates.Not only are plates made faster by my method, therefore, but they aresuperior in performance as Well. The costly shaving operation may beeliminated thereby avoiding the necessity for one of the expensiveshaving machines. It is also clear that my light, strong plates can beshipped cheaper and with less damage in handling.

Figure 8 shows a flat mold press 24 having the limiting stops 26. Fig. 9is a curved mold press 30 also having limiting stops 26. Before pressmolding the unit is subjected to any suitable heat means 32 to make theplastic pliable. Also by penetrating the holes in the plate 18, theplate 18 is greatly strengthened and is also almost impossible ofbending without breaking it. This is most important and particularly incurved printing plates.

Some changes may be made in my method of and means for producingprinting plates without departing from the real spirit and purpose of myinvention, and it is my intention to cover by my claims, any modifiedforms of structure or use of mechanical equivalents which may bereasonably included within their scope.

I claim:

1. A method of making printing plates, comprising, the taking of aprinting shell, applying a thin backing of backing metal to said shellto fill certain depressions of said shell, applying adhesive to thethinly backed shell, placing a sheet of plastic resin material on theadhesivecoated shell back, placing a sheet of perforated light metal onthe free side of said plastic material with an adhesive therebetween,heating the assembled plate and compressing the assembled plate in apress of limited travel, whereby when said assembled and heated plate iscompressed, the plastic material will compensate for irregularities inthe areas of the plate by passing into certain of the perforations ofthe metal plate Without affecting the remainder of the sheet of plasticmaterial, the total area of said perforations being effective when thesheet is compressed in said press to receive any surplus of plasticmaterial but insufficient to weaken the structure of the plate, theentrance of said resin material into said perforations forming anadditional bonding means for securing the resin material and metalsheets together.

2. The method of making printing plates, comprising, the taking of ametallic printing shell, applying adhesive to the back of the printingshell, placing a sheet of resin plastic material on the adhesive-coatedprinting shell; placing a sheet of perforated light metal ion the freeside of said resin material with an adhesive therebetween, heating theassembled plate and compressing the assem- 'bled plate in a press,whereby when said assembled and heated plate is compressed, the resinmaterial will compensate for irregularities in the areas of the platebypassing into certain of the perforations of the metal plate withoutaffecting the remainder of the sheet of resin mate rial, the total areaof said perforations being effective when the sheet is compressed insaid press to receive any surplus of plastic material but insuflicientto Weaken the structure of the plate, the entrance of said resinmaterial into said perforations forming an additional bonding means forsecuring the resin material and metal sheets together.

References Cited in the file of this patent 5 UNITED STATES PATENTS286,821 Hoe Oct. 16, 1883 1,803,548 Drake May 5, 1931 2,114,288 DavisApr. 19,1938 10 2,133,981 Frazier Oct. 25, 1938 Grotf Mar. 7, 1939Cochran June 27, 1944 Boutwell Aug. 15, 1944 Hershberger July 2, 1946Reilly June 26, 1951 SchaflEert et a1. Jan. 8, 1952 Libberton Mar. 24,1953 FOREIGN PATENTS Australia of 1929

